The first workshop accomplished three goals: It 1) Outlined global rooting
patterns for biomes and plant functional types, 2) Discussed the issues
associated with root representations in global models - the issues and
conditions for which they will be important, and 3) Outlined a series of
future modeling exercises as sensitivity analyses and subsequent joint
ecosystem and global simulations.

Site-specific sensitivity runs A detailed sensitivity analysis on a network of well-documented
field stations (and representing the major global biomes) will provide
baseline information to construct a global rooting depth map and provide
a framework to compare model output at variable rooting depths with existing
site data. Output variables will include net primary productivity (NPP),
gross primary productivity (GPP), actual evapotranspiration (AET), transpiration
(Ts), and stream runoff. For models that utilize multiple soil depths,
the exponential Gale and Grigal (1987) equation (1-bd) will be used to
derive the root biomass distribution, where d= soil depth. The experimental
design for the modeling exercise by each group will include 28 potential
sites with variable soil depths (Table 1).
Ideally, a 10y climate database will be developed for each field
station. The climate data needed by modeling groups include daily precipitation,
and minimum and maximum air temperature. Daily shortwave incident radiation
and daylength will be generated from the latitude, longitude, temperature
and precipitation data supplied by the Biome-BGC group. Daily data can
be aggregated for those models that require monthly inputs (e.g. TEM, CENTURY,
MAPSS, CASA). Sub-hourly climate data will be degraded for SiB. In
addition, relative humidity, wind speed and longwave radiation will be
obtained from the Re-Analysis data available on CD-ROM for SiB. Some models
are driven by LAI (MAPSS, CASA) which will be supplied by either the averaged
seasonal LAI from other models that generate it (BGC, CENTURY) or whichever
model provides the most “reasonable” LAI. Models will initialize
the sites as mature ecosystems and go through at least two 10-year climate
cycles for spin-up purposes.

Global simulations Carbon models will be initialized with the global Potsdam climate
data from the PIK exercise, and GCM’s will run on their own climate for
global simulations. Models will be initialized with global rooting
depths provided from a variety of possible sources: 1) Biome-specific
rooting depths as provided from the site sensitivity analyses described
above; (2) A map derived from physical soil constraints (Scholes, IGBP);
or (3) a map derived from inferential (e.g. NDVI) datasets. A subset of
models may examine the biogeochemical consequences of shrub encroachment
globally.